<html>

<head>
    <title></title>
    <script src="https://cdn.jsdelivr.net/npm/vue"></script>
    <style>
        .fade-enter-active,
        .fade-leave-active {
            transition: opacity .5s;
        }

        .fade-enter,
        .fade-leave-to
        /* .fade-leave-active below version 2.1.8 */

            {
            opacity: 0;
        }
    </style>
</head>

<body>
    <div id="demo">
        <button v-on:click="show = !show">
            Toggle
        </button>
        <transition name="fade">
            <p v-if="show">hello</p>
        </transition>
    </div>
</body>
<script>
    new Vue({
        el: '#demo',
        data: {
            show: true
        }
    })
</script>

</html>